Introduction: Evidence on sexual behaviour and COVID-19 shows a change in sexual habits; however, there is no research on the association between mental health and sexual activity. Aim: To examine the relationship between mental health and sexual activity during the quarantine in Spanish adults. Methods: A sample of 305 adults filled out an online questionnaire. Sexual activity was assessed with one question. Anxiety and depression symptoms were assessed using the Beck Anxiety Inventory (BAI) and the Beck Depression Inventory (BDI), respectively. To check associations between levels of both anxiety and depressive symptoms (exposure) and weekly prevalence of sexual activity (outcome), we conducted multiple logistic regression adjusted for control variables (marital status, employment, average household annual income, place of living, pre-COVID-19 sexual activity, current smoking, current alcohol consumption, chronic physical conditions, chronic psychiatric conditions, physical symptoms, and days of confinement). Results: Higher depression level was associated with lower weekly sexual activity in a dose-response fashion in the three implemented models. Participants with higher levels of depression were associated with significantly lower sexual activity in the fully adjusted model (OR: 0.09, 95% CI 0.01–0.61). Mild anxiety-level participants consistently presented significantly lower ORs for lower sexual activity than their minimal-anxiety category counterparts. Particularly, the fully adjusted model showed the lower values (OR: 0.40, 95% CI 0.19–0.84). Conclusion: The results of this study support existing evidence stressing the association between mental health and sexual activity in quarantined adults
